Beneath the surface of China lies the Longyou Grottoes, a breathtaking subterranean marvel featuring grand staircases, expansive hallways, and colossal ten-story columns carved from rock–believed to be over 15,000 years old. This remarkable discovery mirrors Derinkuyu, an enigmatic underground city found in Turkey. Meanwhile, in the American Southwest, secret tunnels linked to Native American lore of the Ant and Snake People are rumored to house covert government UFO programs. And in Egypt and Ecuador, libraries from a lost civilization have long been speculated to be concealed in underground caverns. Might these locations, and others, validate ancient legends of underground realms inhabited by extraterrestrial beings? And if so, what other otherworldly secrets might lie beneath our feet?